Detachable body grounding device



1952 F. A. VAN ATTA ET AL 2,586,

DETACHABLE BODY GROUNDING DEVICE Filed May 10, 1949 *IQJ/ 15 INVENTORS IFloyd A. Van Alia. 23 By Walter G. Leg 0e M Trrij 24 M A 12 PatentedFeb. 19, 1952 DETACHABLE BODY GROUNDING DEVICE Floyd A. Van Atta,Chicago, Ill., and Walter G. Legge, New York, N. Y. said Lcgge assignorto said Van Atta Application May 10, 1949, Serial No. 92,366

6. Claims. 1

Our invention relates to a detachable body grounding device. Moreparticularly, our invention relates to improvements in body groundingdevices whereby electrostatic charges are continuously drained from thebody of a person who may be working, for example, in or near explosivegas mixtures or the like.

It is a matter of common knowledge that electrostatic charges mayaccumulate on a persons body to the point where it discharges as a sparkor are when the body is temporarily grounded. This tendency isespecially noticeable when the relative humidity of the air is low. Ifthe person is working in or near explosive gas mixtures or the like,this spark or are may ignite the explosive mixture. As an illustrationof a practical application of the utility of body grounding devices,mention may be made of its use by surgeons and operating room attendantswhere the patient is being anesthetized with a flammable anestheticagent, as for example ether, ethylene, cyclopropane, or mixturesthereof. When the patient exhales an explosive mixture of the anestheticand air there is danger of explosive from an arc discharge of staticelectricity unless the same has been drained from the bodies of thepersons grouped about the patient. In the past such mishaps haveoccurred, and have resulted in death to the patient.

Several types of body grounding devices have been suggested, but to datethese prior art devices have proved unsatisfactory. For example, it hasbeen suggested that shoes be fabricated from conductive materials suchas graphitized rubber;

however, this raises serious problems in foot comfort since shoesfabricated from such material become uncomfortably warm if worn forconsiderable periods of time. In addition, this plan requires that eachindividual be specially fitted with his or her own pair of shoes.Another unsuccessful attempt at providing a practical body groundingdevice involved permanently securing a metallic plate to the bottom ofthe shoe and connecting this conductor to another conductor placed aboutthe ankle in contact with the skin. The major drawback inherent in thisdevice grew out of the fact that the heavy metal plate was positioneddirectly beneath the ball of the foot to insure contact with the ground,and this resulted in discomfort to the wearer when walking and even whenstanding still. And since the plates were attached to the shoes by nailsor screws theshoes could not conveniently be used for general wear.

It is a principal object of our invention to provide a body groundingdevice which may be quickly and easily detached, which fits all per--sons irrespective of shoe size, and which neither interferes with thecomfort of the wearer nor requires any alterations or disfigurement ofthe wearers shoe.

Another object of our invention is to provide a detachable bodygrounding device which can be electrically dimensioned to within veryclose limits so as to provide optimum electrical characteristics.

Another object of our invention is to provide a body grounding devicewhich is light in weight, durable in use, and inexpensive tomanufacture.

In its broad aspect, our invention comprises a conductive member adaptedto contact the skin of the wearer, a second conductive member which isadapted to be clamped to shoes of various sizes and to underlie theinstep portion of the foot and which is further adapted to press againstthe surface on which the person is standing, and a conductor elementelectrically coupling together the two conductive members. In preferredembodiments of our invention, the first member is fastened about theankle, and includes a resistor of predetermined magnitude placed inseries with the conductor element so that the person is protectedagainst severe and painful electrical shocks should he or sheinadvertently touch a source of high potential current.

In order that our invention may be more fully disclosed, reference ishad to the accompanying drawing which illustrates one form of apparatusembodying the foregoing and such other principles, advantages orcapabilities as may be pointed out as this description proceeds, or asare inherent in the present invention. For purposes of clarity inexposition, the following description is explicit, and the accompanyingdrawing is detailed, but it is distinctly to be understood that saidexposition is illustrative only, and that our invention is notrestricted to the particular details recited in the specification orshown in the drawing.

In the drawing:

Figure 1 illustrates a preferred embodiment of our invention as itappears when attached to the ankle and shoe of a person;

Figure 2 is a front elevational view of the embodiment of Figure 1 as itappears when detached from the wearer;

Figure 3 is a plan elevational view of a portion of the embodiment ofFigure 2;

Figure 4 is a side elevational view taken in section on the line 4-4 ofFigure 3;

Figure 5 is a fragmentary plan elevational view as viewed from the line55 of Figure 2; and

Figure 6 is a perspective view of a modified form of the conductivemember which contacts the skin of the wearer.

Like reference characters designate like parts in the drawing and in thedescription thereof following hereafter.

Referring now to the drawing, the conductive member of our inventionwhich is adapted to contact the skin of the wearer, includes a coiledspring I8 the two ends of which are secured, re-

spectively, to opposite edges of the insulating block II. As shown inFigure 1, the spring I is adapted to fit about the ankle or lower portion of the leg. A cord I2 is threaded through the spring I 0 so thatsaid spring cannot be stretched excessively and thereby deformed whenslipped over the foot or shoe I3.

As best shown in Figures 1 and 2, the conductive member which is adaptedto be removably secured to the shoe I3 includes a spring clip I4 whichlies beneath the overlapping plates I5 and I6. The plate I5 is providedwith a slot I'I through which extends the two pins I8 and I9 whereby theplate I6 is pinned to the spring clip I4. Sufiicient clearance isprovided between the clip I4 and the plate I6 so that the plate I5 isslidable relative thereto. The outer end portions 20 and 2I of theplates I5 and I6, respectively, are bent or otherwise formed intosubstantially hook-shaped configuration. It is these portions 28 and 2Iwhich are adapted to clamp upon the sole 22 of the shoe I3 at the instepportion thereof (Figure 1). The portions 20 and 2| are clamped securelyto the sole 22 by the action of the two helical springs 23 and 24anchored respectively to the rivets 25, 25 on the plate I5,

and the rivets 26, 26 on the plate I6. Advantageously, the springs 23and 24 permit adjustment of the distance between the portions 20 and 2|;therefore the spring clip I4 can be secured to shoes of various sizes.

As is best shown in Figure 4, the end 21 of the spring clip [4 may beflexed. the alternate position shown in dotted outline representing theconfiguration which the clip I4 assumes when attached to the shoe I3 anddeflected in the manner shown in Figure 1. Because of the flexiblenature of the spring clip I4, our invention automatically compensatesfor variations in the height of the'insteps of diiferent shoes, and atthe same time insures a positive connection to ground.

The spring clip I4 is electrically connected to the coiled spring I0 andhence to the ankle of the person wearing the device, through theflexible chain 28. As best shown in Figures 2 and 3, one end of thechain 28 is connected to the plate I6, so that an electrostatic chargedraining down the chain 28 passes on to the plate I6 and from there tothe clip I4 either through the plate I! or rivets I8 and I9, or both.The other end of the chain 28 is secured to the insulating block II.Interposed between and in series with the latter end of the chain 28 andthe coiled spring I0. is a resistor 29, which lies within the bore30,6Xt8nding through the insulating block I I.

The purposes of the resistor 29 is to protect the wearer of the devicefrom severe and painful electrical shocks should the wearer accidentallyground a source of high potential cur rent. Thus, for example, surgeons,nurses and other operating room attendants using our device mayinadvertently contact the electrical circuit of one of the manyelectricall operated machines found in modern day operating rooms. Whileoperating room circuits are usually limited to 110 volts, this potentialis still capable of severely shocking the person if a path of lowresistance connects him to ground. In general, persons can withstand aten milliampere current coursing through their body without sufferingany ill effects. By using a resistor 29 of more than 11,000 ohms, ourdevice will limit the current to less than ten milliamperes (in the caseof a 110 volt potential). At the same time a. resistor 29 of the orderof 11,000 ohms does not interfere in any way with the eflicient drainingof electrostatic charges from the person wearing the device. Hencepersons working in operating rooms, as well as the patient, aresafeguarded.

As a matter. of fact, the resistor 29, in theory at least, could he aslarge as megohms before electrostatic charges would begin to accumulateon the person wearing the device. However, in practice, we prefer thatthe largest resistor 29 be of the order of four or five megohms, so thatthere is no possibilit of any interference with rapid and complete.drainage of electrostatic charges from. persons wearing our device.

While of course each of the various elements of our device could beelectrically dimensioned so that the aggregate resistance would be ofproper. magnitude, by using the separate resistor 29 the precisedegreeof protection against electrical shocks which is desired can be providedboth quickly and accurately. Thus, for example, in most industrialplants line voltages of 440 volts are used. As mentioned previously, itis desirable to limit the current. which will pass through the bodyto nomore than ten milliamperes, should the wearer accidentally touch orgrasp a source of high potential current. By dividing ten milliamperesinto 440 volts, it is apparent that the minimum safe value of resistanceis approximately 44,000 ohms. By inserting a resistor 2.9 of at least/30 'megohms in the bore 38, therefore, the worker is safeguarded.

Advantageously, our device-may be attached without removing the shoe I3,since the coiled spring lflmay be stretched sufiiciently to allow it tobe slipped over the average shoe and on to the ankle of the-wearer. Atthe same time, the-spring I0 is sufiiciently resilient to fit the anklesnugly, so that a good electrical connection between the spring I9 andthe skin of the wearer is assured at all times. After the coil spring I0isin place about the ankle, the plates I5 and I6 are apart sufficientlyto permitslipping the hookshaped portions 20 and 2I thereof over thesole 22 at the instep portion of the shoe I3. When the plates I5 and I 6are released, the helical springs 23 and'24'cause the plates I5 and I6to slide toward each other so that the portions 20 and 2| "clampsecurelyto the sole 22. Advantageously, the coiled spring I0 and the insulatingblock II 'arecompletely hidden beneath the pant leg 3I, whilesubstantially all of the clamping member underlies the instep portion ofthe sole 22, so that only the flexible chain 28 and the portions 28 and21 show.

When the wearer stands,- or otherwise causes theshoe I3 to be placedagainst the ground or floor, the spring clip I4 is flexed upwardly, thispulled V initial tensioning insuring a good contact at all times betweenthe clip M and the ground or floor. At the same time, the spring clip Il does not interfere in any way with Walking or standing because of itsposition beneath the instep portion of the sole 22.

A modification of the conductive member which contacts the skin of thewearer is shown in Figure 6 as including a metallic clip 32 the outerends of which may be flexed apart to permit slipping the clip 32 overthe ankle or other limb. An insulator block 33 is secured to theexterior sur face of the clip 32, and is provided with a groove 34 inwhich the resistor 29 is positioned. One end of the resistor 29! isconnected to the clip 32; the other end to the chain 28 Which isfastened to the block 33. Advantageously, when the clip 32 is secured inplace, it so efiectively covers and contacts a large area of skin as tocause said skin to perspire. The excreted moisture in turn provides asuperior electrical connection between the skin and the clip 32, so thata highly efficient drainage of static electricity is insured.

Having thus fully disclosed our novel detachable body grounding device,and demonstrated its utility by reference to a specific embodimentthereof, we claim as our invention:

1. A detachable body grounding device, comprising: a stretchable,conductive ankle band adapted to be slipped over the foot; a clamp including two metal strips movable relative to each other, the outer endsof said strips terminating, respectively, in a pair of hooks adapted toclamp upon the sole of a shoe at the instep portion thereof, and springmeans connecting said strips and urging said hooks toward each other; ametallic chain linking said clamp and said ankle band; a resistorelement in series with said metallic chain; and a spring clip secured toone of said metal strips and extending downwardly therefrom to connectsaid clamp to ground.

2. A detachable body grounding device, comprising: an ankle bandincluding an insulator block and a coiled metallic spring connected atthe two ends thereof to said insulator block and 3. A detachable bodygrounding device, comprising: a detachable, conductive ankle band, adetachable, conductive clamp adapted to clamp upon the sole of a shoe tounderlie the instep portion thereof, a conductor connecting said ankleband to said clamp, a resistor in series with said conductor, and aconductive spring clip secured to said clamp and extending downwardlytherefrom to connect said clamp to ground.

4. A detachable body grounding device, comprising: a conductive memberadapted to be secured about a limb, a deflectable conductive springadapted to underlie only the instep portion of a shoe, means fordetachably securing said spring to said shoe, electrical conductor meansconnecting said member to said spring, and an electrical resistor inseries with said conductor means limiting the current flow to less thanabout ten milliamperes.

5. A detachable body grounding device, comprising: a first conductivemember, means for removably securing said member to a limb of the wearerin contact with the skin, a defiectable conductive spring member adaptedto underlie the instep portion only of a shoe, detachable clamp means onsaid deflectable member for clamping said defiectable member to saidshoe, and electrical conductor means connecting said first member tosaid deflectable member.

6. A detachablebody grounding device, comprising: a metallic ankle clip,an insulator block secured to said ankle clip, a resistor element oneend of which is electrically connected to said ankle clip, said'resistorelement carried by said insulator block, a detachable, conductive clampadapted to clamp upon the sole of a shoe to underlie the instep portionthereof, a flexible connector connecting the other end of said resistorelement to said clamp, and a conductive spring clip secured to saidclamp and extending downwardly therefrom to ground said clamp.

FLOYD A. VAN ATTA. WALTER G. LEGGE.

REFERENCES CITED ihe following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 620,679 Shryock Mar. '7, 18991,169,428 Rogers Jan. 25, 1916 1,940,491 Freitag Dec. 19,1933 2,239,206Tietig Apr. 22, 1941 2,287,744 Monahan June 23, 1942

